The invention relates to a method for producing tubular bags, a tubular bag produced in accordance with the method and a device for carrying out one of the method steps of the inventive method.
The invention particularly relates to a method for producing tubular bags made from plastic film or from composite film having a plastic layer on the bag content side, having a self-cutting plastic closure attached to the tubular bag, comprising a spout part having a fastening flange, a cutting body, which is movably guided in the spout part, and a screw cover having means for activating the cutting body, wherein the plastic film or composite film is supplied from a supply roll to a bag manufacturing machine and the plastic closure is in each case sealed onto the plastic film or the composite film in a spout region of a tubular bag. In such a method, a plastic film or a composite film is supplied from a supply roll to a tubular bag manufacturing machine, and separately supplied plastic closures are in each case sealed onto the plastic film or composite film in a spout region of a tubular bag.
In the case of flexible containers or, respectively, tubular bags of the aforementioned type, there is the requirement that the film material of the tubular bag has to be suitable for cutting with the cutting body of the plastic closure. At the same time, there is also the requirement that the tubular bag has to be resistant enough to withstand without damage being inadvertently dropped and the ensuing impact on the floor. These two requirements are partially antagonistic. The trouble-free cutting requires relatively brittle materials; whereas materials which have a relatively large elasticity are, however, the only materials which can ensure that the tubular bag will not burst upon impact with the floor or ground.
Film materials of flexible containers have greatly different resilience properties. This relates to the respective degree of possible elongation until breaking, i.e. the elongation at break. Film materials having less elasticity, such as, for example, polypropylene (PP), depending, of course, on the respective material thickness, can generally be cut with a small application of force. Brittle structures, such as aluminum or PET-SiOx, can likewise be easily cut. On the other hand, polyethylene (PE) has an elasticity (elongation at break) of over 800% and therefore presents difficulties in cutting. Polyethylene is however a necessity for break-proof flexible containers (in the case of being dropped as previously mentioned).
In addition, the resilience properties of the different film materials used is also dependent on the processing method used. The values achieved for the elongation at break are typically higher in the longitudinal direction (i.e. in the processing or cutting direction) than in the transverse direction (i.e. transverse to the processing or cutting direction).
It must furthermore be taken into consideration when dealing with composite films having layers of different materials that the material with the highest elasticity, i.e. precisely, for example, polyethylene, determines the effective elongation at break when a failure of the present composite occurs (in the cutting region).
Because tubular bags of the aforementioned type are used for the transport and storage of sensitive contents, such as, for example, foodstuffs, the integrity of the packaging must, of course, also be maintained until being opened by the consumer. It is therefore often the case that the flexible containers must also meet a number of other requirements in this regard.
Film materials are thus used which meet all of the aforementioned requirements to the greatest possible extent. These are then typically precisely those film materials or composite materials which, on the one hand, meet the requirements for strength, impermeability and hygiene and are however, on the other hand, also specifically designed to be easily or at least relatively easily cut. An example of the layered design of a commonly used composite film is depicted in FIG. 1. Overall, the ability of the cutting body disposed in the spout part to cut properly often continues, however, to be a problem. This can also generally be attributed to the fact that different stress ratios of the (remaining and not yet completely cut) film material, which usually can only be manipulated with a great deal of difficulty, are encountered during the course of the cutting operation. Further options for improving the capacity of the tubular bag to be cut open in a controlled manner are therefore sought. Several known options for improving the capacity of the tubular bag to be cut open consist of weakening the layered structure in the region of the cutting zone in a targeted manner, for example by means of laser scribing or by means of other partial perforations applied beforehand.